The present invention relates to the fabrication of integrated circuits by chemical vapor deposition in a vacuum chamber. More particularly, the invention relates to a method and apparatus that enable the formation of high quality CVD films using both low temperature (e.g., about 400.degree. C.) and high temperature (e.g., above about 580.degree. C.) processing. The present invention is particularly useful in the deposition of TEOS-based (tetraethylorthosilicate) and silane-based chemistries including PECVD and SACVD deposition of silicon oxide, silicon nitride, silicon oxynitride and amorphous silicon as well as doped silicon oxides such as boron phosphorus silicate glass, phosphorus silicate glass and fluorine-doped silicate glass. The present invention may also, however, be used with other deposition chemistries.
One of the primary steps in the fabrication of modem semiconductor devices is the formation of a thin film on a semiconductor substrate by chemical reaction of gases. Such a deposition process is referred to as chemical vapor deposition or CVD. Conventional thermal CVD processes supply reactive gases to the substrate surface where heat-induced chemical reactions take place to produce a desired film.
An alternative method of depositing layers over a substrate includes plasma enhanced CVD (PECVD) techniques. Plasma enhanced CVD techniques promote excitation and/or dissociation of the reactant gases by the application of radio frequency (RF) energy to a reaction zone near the substrate surface, thereby creating a plasma. The high reactivity of the species in the plasma reduces the energy required for a chemical reaction to take place, and thus lowers the temperature required for such CVD processes as compared to conventional thermal CVD processes. The relatively low temperature of some PECVD processes helps semiconductor manufacturers lower the overall thermal budget in the fabrication of some integrated circuits.
Semiconductor device geometries have dramatically decreased in size since such devices were first introduced several decades ago. Since then, integrated circuits have generally followed the eighteen month/half-size rule (often called "Moore's Law"), which means that the number of devices that will fit on a chip quadruples every eighteen months. Today's wafer fabrication plants are routinely producing integrated circuits having 0.5-.mu.m and even 0.25-.mu.m features, and tomorrow's plants soon will be producing devices having even smaller geometries.
Such decreases in size have been made possible in part by advances in technology associated with semiconductor manufacturing equipment, such as the substrate processing chambers used for PECVD processing. Some of the technology advances include advances that are reflected in the design and manufacture of certain CVD deposition systems in use in fabrication facilities today, while others are in various stages of development and will soon be in widespread use throughout the fabrication facilities of tomorrow.
One technology advance commonly used in today's fabrication facilities includes the use of a PECVD technique often referred to as mixed frequency PECVD in which both high and low frequency RF power are employed to generate a plasma and to promote ion bombardment of a substrate. One such mixed frequency method couples both high and low frequency RF power to a metal gas distribution manifold that acts as a first electrode. In this method, application of the high frequency RF power is the primary mechanism that dissociates the reactant gases while application of the low frequency RF power promotes ion bombardment of a substrate positioned on a grounded substrate support that also functions as a second electrode. Another mixed frequency method couples high frequency RF power to a gas distribution manifold (first electrode) and couples low frequency RF power to a substrate holder (second electrode).
Another technology advance used in some currently available PECVD deposition chambers includes the use of conical holes in the gas distribution manifold to increase the dissociation of gases introduced into a chamber. A more detailed description of such conical holes is contained in U.S. Pat. No. 4,854,263, entitled "INLET MANIFOLD AND METHODS FOR INCREASING GAS DISSOCIATION AND FOR PECVD OF DIELECTRIC FILMS," and having Mei Chang, David Wang, John White and Dan Maydan listed as co-inventors. The '263 patent is assigned to Applied Materials, the assignee of the present patent application, and is hereby incorporated by reference in its entirety.
An example of a technology advance that is more recent than those noted above is the use of ceramics in a CVD chamber to allow the reactor to be used in high temperature operations. One CVD chamber that is specifically designed for such high temperature processing and includes a ceramic heater assembly among other features of the chamber is described in the Ser. No. 08/800,896 application noted above.
Advances in technology such as those just described are not without restrictions. For example, while mixed frequency PECVD techniques have proved to be very beneficial in a variety of applications, the simultaneous application of the high and low frequency waveforms must be controlled to avoid interferences which can result in high voltages and arcing at the gas distribution manifold. Arcing may be evidenced by a glow within the holes in the gas distribution manifold, and by a reduction in deposition rate as the amplitude of the high frequency voltage is increased. Arcing is typically avoided using one or more of the following techniques: maintaining the pressure within the vacuum chamber above a de minimis level for a particular process, operating with the low frequency RF power set at a value less than 30% of the total RF power, and/or reducing total RF power.
In the past, experiments had been performed in which conical holes were employed in a mixed frequency PECVD chamber having both the high and low frequency RF power sources connected to the gas distribution manifold. In these experiments, it was found that the arcing problem was further increased to the point that it substantially interfered with film deposition. Thus, all mixed frequency PECVD systems known to the inventors use straight, rather than conical, holes in the gas distribution manifold.
Accordingly, it is desirable to develop technology for substrate deposition chambers that enables semiconductor manufacturers to simultaneously take advantage of conical holes and mixed frequency PECVD deposition techniques.